1. Field of the Invention
This invention relates to a shadow mask of a color cathode ray tube and, more particularly, to improvement of a supporting structure for holding the shadow mask therethrough on the panel.
2. Description of the Related Art
A shadow mask type color cathode ray tube is composed of a panel having a substantially rectangular faceplate, a substantially cylindrical neck in which an electron gun is arranged and a funnel extending from the neck. Formed on the inner surface of the faceplate is a phosphor screen which emits red, blue, and green light rays when electron beams land thereon. A rectangular shadow mask made of a thin metal plate and having a large number of slit apertures is arranged in the panel such that it opposes the phosphor screen. This shadow mask is fixed in place by welding a peripheral portion thereof to a rectangular frame. Supporting structures, which are resiliently deformable, are fixed in place by welding to the corners of the frame. The frame is held in the panel as the resiliently deformable supporting structures are attached to panel pins fixed on an inner surface of the skirt. The elastically deformable supporting structures serve to hold the shadow mask, thereby preventing discoloration, which is caused by a relative displacement between the apertures of the shadow mask and the phosphor stripes of the screen, when the shadow mask and the frame are heated and expand. Therefore, when the cathode ray tube begins operating, the shadow mask is moved slightly, by the supporting structures, toward the phosphor screen, thereby making it possible to obtain a high color purity.
The supporting structures which hold the frame having the shadow mask welded thereto on the panel are indicated in U.S. patent application No. 844,553 now U.S. Pat. No. 4,723,088; U.S. patent application No. 878,680 now U.S. Pat. No. 4,728,853 and U.S. patent application No. 120,982 and in U.S. Pat. No. 4,652,792 and in attorney dockets No. 62P850, identified by Ser. No. 07/149,049, and 63P069, filed Mar. 2, 1988 as Ser. No. 163,100 now U.S. Pat. No. 4,886,997,and a supporting structure as shown in FIGS. 1 and 2 is disclosed in U.S. Pat. No. 4,723,088. As shown in FIG. 1, supporting structure 1, which is made by bending a stainless plate in a U-like configuration, has fixed section 4 fixed by welding to frame 3, connecting section 2 in a U-like configuration and engaging section 5 with hole 6 into which a panel pin is inserted. Supporting structure 10 shown in FIG. 2 comprises fixed plate 13 fixed by welding to frame 12 and movable plate 14. Movable plate 14 has connecting section 16 and engaging section 17 formed by bending a plate section extending from welded section 15 welded to fixed plate 13. A hole 18 is formed in engaging section 17. The frame having supporting structure 1 or 10 fixed thereto is mounted to and dismounted from the panel several times during the manufacturing process of color cathode ray tubes. Hence, the supporting structures must be in such a shape that they do not suffer plastic deformation when they are mounted and dismounted repeatedly. Supporting structures 1 and 10 shown in FIGS. 1 and 2, respectively, are formed in shapes less susceptible to plastic deformation. However, these supporting structures have a drawback that they are easily deformed by an external impact applied to the color cathode ray tube. More specifically, as shown in FIG. 1, when a force in the direction of the arrow F1 is applied from a periphery of hole 6 to engaging section 5 by an external impact and a force in the direction of the arrow F2 is applied from frame 3 to fixing section 4, supporting structure 1 is deformed such that the radius of the circular part of first side end portion 7 of connecting section 2 becomes larger and the radius of the circular part of second side end portion 8 becomes smaller. As a result, connecting section 2 is deformed permanently. Referring to FIG. 2, supporting structure 10, having a construction such that two metal plates are welded together, is higher in strength to withstand a force resulting from an impact applied to connecting section 16 and is thus prevented from being twisted and deformed permanently to the maximum extent feasible. However, if a force in the direction of the arrow F4 is applied to fixed plate 13 and a force in the direction of the arrow F3 is applied to movable plate 14, there is still a possibility that connecting section 16 is twisted and deformed permanently just as with supporting structure 1. With these supporting structures, if one wishes to decrease the amount of plastic deformation, it is necessary to increase the thickness of the metal plate. If the thickness of the metal plate is increased, it becomes necessary to apply a greater force to the supporting structures in mounting and dismounting the frame in the manufacturing process of color cathode ray tubes. Therefore, a longer time is taken in mounting and dismounting the frame and thus, the efficiency in mounting and dismounting the frame is decreased. Further, if the thickness of the metal plate of the supporting structures is increased, a large force is applied to the shadow mask when the frame is mounted and dismounted and the relatively thin shadow mask is deformed. Such being the situation, it has been desired that a supporting structure should be materialized that assures high work efficiency in the manufacturing process and suffers a reduced amount of deformation due to a twist which occurs when an impact is applied.